1. Field of the Invention
This invention relates to a PCM (pulse code modulated) audio signal reproducing apparatus, and more particularly is directed to an 8 mm video tape recorder also adapted for recording a PCM audio signal.
2. Description of the Prior Art
Standardization of a co-called 8 mm video tape recorder has been proposed. According to such standardization represented generally in U.S. Pat. No. 4,551,771 having a common assignee herewith, the recording and/or reproducing of a video signal on and/or from a magnetic tape is carried out by first and second rotary magnetic heads which are mounted on a rotary tape guide drum at respective locations having an angular spacing of 180.degree. therebetween. The magnetic tape is helically wrapped around the periphery of the tape guide drum over an angular range of 221.degree. and is normally transported longitudinally so that the rotary heads alternately scan skewed or slant tracks on the tape. In an interval of 180.degree. within the tape wrapping angle of 221.degree., the rotary heads normally record or reproduce a video signal in the skewed tracks on the magnetic tape. In the remaining interval of 36.degree., that is, an overscan section of each track, an audio signal, which is pulse-code-modulated and time-base-compressed, is recorded on and/or reproduced from the magnetic tape by the same rotary.
Alternatively, and as disclosed in detail in U.S. Pat. No. 4,542,419 which also has a common assignee herewith, it is possible to establish a so-called audio-use mode in which the area of each track corresponding to the angular range of 180.degree. is divided equally by 5 and the PCM audio signal may also be recorded in a selected one of these divided portions during scanning of each track. More specifically, the whole area of each track is divided into 6 segments each corresponding to an angular range of 3620 , and first to sixth track channels are formed by the similarly situated segments of the respective skewed tracks, whereby the PCM audio signal can be recorded in any desired track channel.
Upon reproducing operation of the 8 mm video tape recorder, it is necessary to determine whether the tape being played is a so-called video tape or a multi-channel PCM tape. If it is a multi-channel PCM tape, it is desirable to cut-off or mute the monitor picture. For example, if a PCM audio signal is recorded in one of the channels of the tape on the area of the tape in which the video signal would otherwise be recorded, a noise bar of band-shape corresponding to the PCM audio signal recording area appears on the reproduced picture displayed by the monitor. If it can be determined that a PCM audio signal is recorded on the multi-channel PCM recording area, such strange picture or display can be avoided by muting the video signal to the monitor.
As one of the methods for identifying a tape on which there is a multi-channel PCM recording, it has been proposed that an identifying pilot signal in the form of a continuous wave having a suitable frequency, for example, 228.748 kHz, be recorded on the PCM audio signal recording area in a frequency multiplexed manner.
When such tape having a multi-channel PCM audio recording thereon is reproduced, in which case a video signal is not reproduced, it would be useless to detect the presence or absence of a high frequency video signal in the reproduced signal for controlling a muting circuit of the video signal reproducing circuit. In other words, when the video signal is not recorded on the tape but a PCM audio signal is recorded on the tape in the multi-channel PCM audio format, such state may be mistaken as a case in which the video signal is recorded and, therefore, the muting circuit of the video signal reproducing circuit can not be operated to mute the video signal.